When "Thor" was released in 2011, the film became far more popular than anyone imagined it would be. While this was certainly due in part to the engrossing story line, fantastic visuals, and the steady popularity of superhero films, the cast was a major reason for the film's tremendous worldwide success. Tom Hiddleston was relatively unknown before taking on the role of Loki in "Thor," but he skyrocketed to international stardom after his compelling performance. Chris Hemsworth had a similar story, and he quickly became a favorite all over the globe as well. On the other hand, Natalie Portman was already well known, even though her character was slightly less prominent than the two godly brothers. Perhaps one of the reasons "Thor" was so successful was that Thor and Loki were both portrayed by actors unfamiliar to most viewers. Hollywood loves fresh faces, especially when those faces belong to attractive young men.

Despite Hemsworth's lack of experience, the character of Thor in both "Thor" and "Thor: The Dark World" was a perfect fit for him. After all, ever since his comic book debut in 1962, Thor has always been a rugged, good-looking hero, and Hemsworth is the very embodiment of that ideal. But physical appearance isn't the sole reason Hemsworth fits the role of Thor. As the fictionalized version of the god of thunder from Norse mythology, Thor is a force to be reckoned with, but he has unusually human qualities for a being with such incredible power. Thanks to his raw talent and his real-life personality, Chris Hemsworth manages to strike the perfect balance between bold hero and sensitive good guy.

Hemsworth's naturally bright appearance is also an excellent contrast to the significantly darker and more brooding image of costar Hiddleston, in the role of Thor's far-from-benevolent adopted brother, Loki. The two actors even claim to feel like brothers in real life, and this bond does wonders for their onscreen chemistry—after all, in spite of their very evident differences and conflicts, Thor and Loki still share a deep bond.

Then there's Natalie Portman, one of Hollywood's most talented and cherished actresses. Ever since her 1994 debut as Mathilda in "Léon: The Professional," she has portrayed a wide variety of characters, from Padmé Amidala in the three "Star Wars" prequels to the brave runner-turned-revolutionary in "V for Vendetta." In "Thor," she portrays an astrophysicist named Jane Foster, and she reprises that role in "Thor: The Dark World." Portman is an excellent choice for this unique role. Unlike the stereotypical female scientists common in so many movies, Jane Foster was supposed to be beautiful; however, as a serious scientist, she wasn't supposed to look as if she put more stock in her appearance than in her work. Portman certainly fits the bill for a classic beauty with an aura of intelligence.

Kenneth Branagh didn't cast Portman solely for her appearance, of course. Just as he cast Hemsworth as Thor because of his personality and raw talent, he cast Portman because he had faith in her ability to bring unusual characters such as Jane Foster to life. In fact, she signed on long before a script for the film was even created, and Kenneth Branagh gave her plenty of freedom when it came to creating the character of Foster. Without Natalie Portman's involvement, Jane Foster could have ended up as a very different character, and it's clear from both "Thor" and "Thor: The Dark World" that she has truly made the quirky scientist her own.

Even though it's obvious that Natalie Portman and Chris Hemsworth were appropriately cast in "Thor: The Dark World" because it would have been next to impossible to replace them, that's not the only reason they were ideal choices for the characters they portray. Both actors have incredible talent as well as an ample supply of natural good looks and charm. Of course, it's also clear from the chemistry between Portman and Hemsworth that their casting was appropriate. From the moment they first meet in "Thor" to their dramatic reunion in "Thor: The Dark World," Thor and Jane Foster seem to have been made for each other. Thor is a boisterous and sometimes overtly physical young man, and, with her serious and quiet demeanor, Jane Foster is his exact opposite. In real life, Hemsworth and Portman aren't much different from Thor and Jane Foster, which brings a certain level of honesty and realism to their portrayals of these characters.